Reduction of Ln₂Ti₂O₇ Layered Perovskites: A Survey of the Anionic Lattice, Electronic Features, and Potentials

Abstract

The reduction of the layered perovskites Ln 2 Ti 2 O 7 (LnTO, with lanthanide Ln= La, Pr, Nd) was studied with the aim to shift the UV photocalytic activity for water splitting in the visible range by Ti 3+ donor doping. For all phases, after reduction by CaH , the absorbance is extended beyond the UV-vis region, giving rise to a gap-like edge in the mid-infrared at ~0.4eV with a dark coloration of the samples. When the precursor with Ln= La was reduced under high temperature H 2 flow, we found a progressive nanotexturation down to 300 nm, which is responsible for a degree of Ti 3+ segregation at the surface. Magnetic measurements, thermal analysis and powder neutron diffraction (PND) reveal that the sample reduced by both routes have a similar amount of anion vacancy with δ = 0.27 (in La 2 Ti 2 O 7-δ). It represents a limited topotactic reduction stage, prior to the reconstructive reduction into La 5 Ti +3.8 5 O 17 observed in more sever reducing conditions. For the sample reduced by CaH 2 , a minor amount of hydride appears to be incorporated (~0.02 H per FU), with a Ti 3+-Hbonding observed by HYSCORE electron paramagnetic resonance (EPR) and density functional theory (DFT) calculations. Preliminary electrocatalysis tests show a promising anodic activity for water splitting hydrogen evolution with a voltage onset as low as 0.6V vs. RHE.

Electrophoretic Deposition of Chitosan Films Doped with Nd2Ti2O7Nanoparticles as Protective Coatings against Corrosion in Saline Solutions

“…The interreticular distances d 00l coincide with the reference data JCPDS #33-0942 corresponding to the Nd 2 Ti 2 O 7 monoclinic [28,29]. It has been reported that Nd 2 Ti 2 O 7 has a thermodynamically stable stratified perovskite structure [30]. Figure 4 shows the FT-IR spectrum of the Nd 2 Ti 2 O 7 nanoparticles.…”

Noble Metal‐Free Nanocatalysts with Vacancies for Electrochemical Water Splitting

“…It is observed that the inert basal planes are activated due to the introduction of selenium vacancies, which provide the active sites for hydrogen adsorption to enhance the HER. Similar work of using reductive annealing has also been reported for the effective creation of oxygen vacancies in CaMnO 3 and Ln 2 Ti 2 O 7 perovskites …”

New chemistry of transition metal oxyhydrides

“…We further note that it is not yet possible to predict whether an oxygen-deficient product or oxyhydride product will result; for example, an anatase TiO 2 film simply gives a dark-colored TiO 2– x phase when treated with CaH 2 [ 36 ], whereas BaTiO 3 gives the oxyhydride. La 2 Ti 2 O 7 contains only minute amounts of hydride [ 37 ].…”